A large number of commercial and factory plant roofs are of a flat roof design wherein the roofing material itself is often of a builtup asphalt and in more modern systems of a single ply EPDM elastomeric sheet or membrane. In terms of securing a single ply EPDM membrane to the roof itself, one design utilizes a mechanical ballast system that uses a layer of stone over the membrane. While the ballast system is least expensive it has a disadvantage of being quite heavy (approximately 10 pounds per square foot) thus requiring a heavy roof support structure and in addition the roof slope cannot exceed 10%.
Adhered roof membrane retention systems suffer from the cost penalty while mechanical fasteners and related fastening systems generally require fixation to the roofing substrate via mechanical fasteners. There are two basic kinds of mechanical fasteners namely, membrane penetrating and non-penetrating ones. Each of these types of fasteners has a number of favorable features and each of them is also subject to various drawbacks and disadvantages.
Mechanical fastening systems of the pentrating type generally require fixation to the roofing substrate by a metal fastener with metal or rubberized nailing strips. U.S. Pat. Nos. 4,445,306; 4,074,501; 4,455,804; and 4,467,581 are examples of penetrating type fastening systems in which various rigid and semi-rigid members are used to secure the membrane to the roof. These systems require openings to be formed in the membrane either for receiving a fastening plate or by the attaching anchoring members.
Examples of a non-penetrating type fastener is shown in German Patent Publication 24 33 669 in which the membrane fastener comprises a lower disc which is attached to a roofing substrate by an anchoring member. The roofing membrane is fitted over the lower disc and an upper disc is snapped over the lower disc to perfect the fastening and exert a sealing effect. In another embodiment of this Patent Publication, a plug is driven into the upper disc to expand the body thereof into an annular space provided in the lower disc to anchor the upper disc thereto. Another type of non-penetrating fastening system is shown in U.S. Pat. No. 3,426,412 which has a flexible fastening cover which is snapped over a base member to trap the membrane therebetween. Another embodiment shown in this U.S. patent uses a plug-like member which is snap-fitted into a recess formed in a lower member which is rigidly connected to the roof to trap and clamp the membrane therebetween.
Although both the penetrating and non-penetrating type fastening system do work satisfactory for many applications, it is desirable to have a non-penetrating system for certain applications to eliminate piercing the membrane. Also such a fastener can be installed in a minimum amount of time and without requiring skilled labor, and the fastening element can be securely retained in clamping engagement with the trapped membrane to reduce the accidental disengagement thereof upon the membrane experiencing severe uplift wind forces.